Communication networks include a collection of resources that are employed to transport user information from source nodes to destination nodes. The resources include switching nodes and communication links. In a packet switching network, user information takes the form of packetized digital data. The user information is carried in discrete individual packets, and each individual packet carries its own destination address along with at least a portion of the user information. Switching nodes evaluate the destination addresses to determine how to appropriately route the packets.
Services providers which operate communication networks as well as their users benefit from improved network efficiency. Service providers want improved efficiency because they can generate greater revenue by transporting a greater amount of user information using a given collection of network resources. Users want improved efficiency because the costs of providing the network resources can then be spread over a greater number of user information transfers to lower the costs of transporting any single item of user information.
Unfortunately, conventional packet switching and other networks are operated in a relatively inefficient manner. Inefficiencies are particularly onerous in connection with the consumption of communication links to transport redundant or nearly redundant user information. The portion of link bandwidth which is used to transport redundant or nearly redundant user information cannot be used to transport more independent user information, and this results in an inefficient use of network resources.
The transportation of redundant or nearly redundant user information results, at least in part, from the tendency of conventional networks to view the processing of user information as a user responsibility. For example, when a single source node wishes to broadcast certain user information to a number of destination nodes, the source rode has the responsibility of duplicating and separately transmitting packets as needed for each destination node. Many network communication links and switching nodes repetitively handle substantially the same data merely addressed to different destinations.
Likewise, error detection and correction of user information is conventionally performed by users on an end-to-end basis. A source node encodes user data so that certain errors may be detected and perhaps corrected. The destination node decodes the encoded data to check for errors. In typical data communication protocols, when errors cannot be corrected the destination node returns a message to the source node requesting repetition of at least certain portions of the user data. The conditions which lead to errors in the first place may still be present during a repeated transmission, and a good likelihood exists that user data is transmitted several times before the destination node can make a reconstructed error-free version of the user data.
These are only two of many examples where conventional communication network resources are inefficiently utilized.
While the problems associated with the inefficient use of network resources plague a wide variety of communication networks, they have more serious consequences in networks which rely on RF communication links. Such links may, for example, trunk communications between ground stations and satellites, between pairs of satellites, or between pairs of ground stations. RF communication links are constrained to using an assigned portion of the electromagnetic spectrum, and this assigned portion is a scarce resource which should be managed efficiently. In addition, the efficient use of RF communication links dictates decreasing link margins to increase communication traffic thoughput. When a desirable balance is found between link margin and communication traffic throughput, noise will cause data errors on occasion. These data errors lead to the redundant and inefficient use of communication links through end-to-end error detection and correction schemes.